Revert of [Android] Disable enhanced bookmark opt-in flag. (patchset #1 id:1...

Revert of [Android] Disable enhanced bookmark opt-in flag. (patchset #1 id:1 of https://codereview.chromium.org/610443002/)

Reason for revert:
M39 branched, so re-enable the flag on trunk.

Original issue's description:
> [Android] Disable enhanced bookmark opt-in flag.
>
> We won't launch this feature for M39, so disable public opt-in flag.
>
> BUG=416664
>
> Committed: https://crrev.com/5da932e693169900a4a4be346446788aa1944eeb
> Cr-Commit-Position: refs/heads/master@{#296825}

TBR=yfriedman@google.com,tedchoc@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=416664

Review URL: https://codereview.chromium.org/612203002

Cr-Commit-Position: refs/heads/master@{#297273}

chrome/browser/about_flags.cc

@@ -2043,6 +2043,10 @@ bool SkipConditionalExperiment(const Experiment& experiment,
                                FlagsStorage* flags_storage) {
   if (experiment.internal_name ==
       std::string("enhanced-bookmarks-experiment")) {
+#if defined(OS_ANDROID)
+      // On Android, user can opt in.
+      return false;
+#else
     CommandLine* command_line = CommandLine::ForCurrentProcess();
     // Dont't skip experiment if it has non default value.
     // It means user selected it.
@@ -2050,6 +2054,7 @@ bool SkipConditionalExperiment(const Experiment& experiment,
       return false;
 
     return !IsEnhancedBookmarksExperimentEnabled(flags_storage);
+#endif
   }
 
   if ((experiment.internal_name == std::string("manual-enhanced-bookmarks")) ||